1. Field of the Invention
The present invention relates to an object tracking apparatus, an object tracking method and a recording medium for tracking movements of an object by detecting the object on real-time basis based on inputted images, which are acquired time-sequentially and successively, without inputting information on the initial position of the object.
2. Brief Description of the Related Art
Tracking a moving object is a method to detect a displacement in position/posture of the object between two neighboring frames of time-sequential image data. Basically a real-time object tracking can be realized when the displacement between two neighboring frames is calculated at a rate faster than the video rate (30 frames per second). However, almost all proposed methods in the past did not consider how to acquire the initial position of the object, which plays a role of a starting point of the tracking. Consequently, these methods are used only when the initial position of the object is already known.
In the case of tracking the object of which initial position is unknown, a method where a three-dimensional object recognition method, as a pretreatment, is combined with the object tracking method is proposed. However, since the three-dimensional object recognition method has to detect position/posture of the object from the whole scene where a huge amount of calculations in order of O(MN) to O(M3N3), (M and N are respectively numbers of features of a scene and a model) are required, tracking the object at the video rate is difficult. Here the function O(f(n)) is a function to express asymptotic time complexity, when the n number of data are inputted. In other words, even a tracking system combined with the object recognition method, cannot deal with a continually moving object (a non-stop moving object).
It is inevitable that the object is sometimes lost during tracking the object due to occlusion phenomena or the like in the movement tracking process. In conventional methods, however, it is difficult to resume the tracking process once the object is lost.
Practically used movement tracking systems are based on very simple algorithms such as background differential methods or the like. Since these methods can process data at very fast rate, it is not required to detect the initial position of the object, but functions attained by these methods are limited. For example, it is difficult for these methods to estimate 6 degrees of freedom, i.e. position/posture of the object in a three-dimensional space.
As mentioned above, since conventional object movement tracking methods require information on the initial position of the object to be tracked, an object of which initial position is unknown or a continually moving object cannot be tracked. In addition tracking process cannot be recovered once the tracking is failed on the way. As measures against the problems mentioned above, although a lot of movement tracking methods have been proposed, they are applicable only to limited fields except simple algorithms such as background differential methods.